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1.1.6 Tracking empty cross amp
The tracking empty cross signal (hereafter, TEC signal) is the signal amplifying TE signal for 4 times and used to find an
empty cross point of tracking error. The purpose for finding the empty cross point is;
1 To use for track count at carriage movement and track jump
2 To use for detecting direction of lens movement at tracking close (used in a tracking brake circuit described later)
The frequency range of TEC signal is 300 Hz - 20kHz, and voltage TEC=TE level X 4.
That is, TEC level is 4.62V as calculated, and this level is over D range of an operation amp and so that the signal is
clipped, but only empty cross point is used in CD LSI, so there is no problem.
1.1.7 EFM circuit
EFM circuit is the circuit for converting RF signal into "0" "1" digital signal. AGCO signal output from the number 116 pin
is AC-combined, input to the number 114 pin, and supplied to EFM circuit.
Since RF vertical asymmetry occurred because of the lack of RF signal by a scratch or dirt on a disc, and quality
variation of disc production is not deleted only by AC-combination, reference voltage ASY of EFM comparator is
controlled, taking advantage of the fact that the occurring rate of "0" "1" in EFM signal is 50%. In this way, the
comparator level is always around the center of RFO signal. This reference voltage ASY is generated with passing EFM
comparator output through LPF. EFM signal is output from the number 111 pin.
RFI
114
VDD
40K
40K
Fig.4 EFM
5
6
VDD
+
-
+
-
100K
6
7
UPD63763AGJ,
UPD63761AGJ
EFM signal
+
-
CX-3168
7
8
ASY
112
EFM
111
2K
8
A
B
C
D
E
F
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